Baseboard Heater Calculator — What Size Heater for a Room?
Enter your room size, ceiling height and insulation to get the baseboard wattage you need and the heater length to buy. No sign-up, no data stored.
Heater size
How baseboard heater size is estimated
- Room area (sq ft) = length x width.
- Watts = area x watts per sq ft (8-15 depending on insulation and climate).
- Ceiling factor = +10% per extra foot above 8 ft.
- Heater length (ft) = watts ÷ 250 W per linear foot.
The 10-watt rule is a quick sizing standard for electric resistance heat. A real Manual J heat-load calculation is more accurate, but this method gets you to the right heater within one size either way for typical rooms.
Room size → baseboard heater reference
10 W/sq ft, 8-ft ceiling, 250 W per linear foot.
| Room | Area | Watts | Heater |
|---|---|---|---|
| 8x10 bathroom | 80 sq ft | 800 W | 1,000 W (4 ft) |
| 10x10 bedroom | 100 sq ft | 1,000 W | 1,000 W (4 ft) |
| 12x12 bedroom | 144 sq ft | 1,440 W | 1,500 W (6 ft) |
| 12x14 living room | 168 sq ft | 1,680 W | 1,500 + 500 W (7 ft) |
| 14x20 great room | 280 sq ft | 2,800 W | 2 x 1,500 W (12 ft) |
Last updated: October 2026 · Confirm with a heat-load calculation for additions, vaulted ceilings or rooms with many windows. Electric baseboard is 100% efficient, so wattage equals heat output.
Baseboard heater FAQ
Roughly 10 watts per sq ft for a standard 8-ft ceiling in a moderate climate, 8 W for well-insulated spaces, and up to 12-15 W for poorly insulated rooms or colder zones. It is a planning rule, not a substitute for a heat-load calc.
A typical electric baseboard puts out 250 watts per linear foot - a 1,500-W heater is about 6 ft long. For a 12x14 room needing ~1,700 W, you would install about 7 ft of baseboard, often split between two walls.
You can, but it will run continuously and still feel cold on the worst days. Oversizing by 10-15% is fine since thermostats cycle - undersizing is the mistake that leaves rooms drafty in January.
Yes. Each extra foot of ceiling adds ~10% heat load. Big windows or poor glazing add another 10-20%. Our calculator folds both into the wattage so you are not sizing for a room that loses heat faster than it gains it.
Yes - placing them under the window is best: rising warm air meets the cold draft from the glass, cutting condensation and keeping the room even. Never block the heater with furniture or long curtains.
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What Size Baseboard Heater Do I Need?
Wattage rules, climate factors and placement for electric baseboard.
Read the guide →